Recently, a phased array system for steering the direction of an antenna beam at a high frequency, in particular, in a milli-wave band has been used, for example, in the fields of communication and sensor. The phased array system includes, for example, a phase shifter. The phase shifter is desirably capable of shifting the phase of a signal in a range of 0° to 360° while maintaining the amplitude thereof.
Technologies described below are known as technologies related to such a phase shifter. For example, a variable phase device including a transmission line, a vector synthesizer, and a phase controller is known. The transmission line outputs signals having phases orthogonal to each other through a pair of output ports. The vector synthesizer includes first and second transistors connected with a pair of respective output ports so that a parasitic capacitor acts as a load impedance for the transmission line. The vector synthesizer amplifies, through the first and second transistors, signals output in phases in accordance with the load impedance from the pair of output ports of the transmission line, and synthesizes the amplified signals. The phase controller controls the phase of the output signal synthesized and output by the synthesizer by controlling amplification operations at the first and second transistors of the synthesizer.
Technologies described below are known as technologies related to an amplification circuit applicable to a phase shifter. For example, a polarity switching amplification circuit including first and second amplification transistors, a transformer, and a polarity switching controller is known. Unbalanced input signals (single-ended signals) are input to the first and second amplification transistors. The transformer includes a primary winding wire and a secondary winding wire. Output signals from the first and second amplification transistors are input as balanced signals (differential signals) to the primary winding wire and output from the secondary winding wire. The polarity switching controller turns on one of the first and second amplification transistors while turning off the other amplification transistor.
A known endless phase shifter that is capable of endlessly shifting the phase angle of 360-degree includes a unit for bifurcating an input signal into two signals having a phase relation of 90°, first and second modulation units having configurations identical to each other, and a unit for synthesizing output signals from the first and second modulation units. The first and second modulation units each include a unit for inverting a phase by 0° or 180°, and a unit for controlling a signal level independently from the phase inverting unit. The first and second modulation units each modulate each of the two bifurcated signals to a signal at a predetermined level having a phase relation of 0° or 180° relative to the bifurcated signal.
The related techniques are disclosed in, for example, Japanese Laid-open Patent Publication Nos. 2014-110492, 2014-199966, and 58-47336.